SEN. GEORGE MCGOVERN apparently did something unconscionable the other day: He expressed concern over the atrocities committed upon the Cambodian people by their own wretched leaders and raised the question -- no more than that -- of whether some sort of international rescue mission might not be indicated. The response, in the still-rancid aftermath of this country's Vietnam trauma, was as ungenerous and vindictive as it was predictable. Mr. McGovern, it is now being argued in certain circles uncongenial to the senator's general philosophy, has forfeited the right to complain about what goes on anywhere in Indochina.

Why? Because he is a liberal, one of those bleeding-heart types, you know, who 1) led us into the war in an excess of simple-minded enthusiasm for the exercise of American influence around the world, and 2) sabotaged the war effort when they began to see its carnage as immoral. "McGovern the Hawk," cried The Wall Street Journal, which found a "truly mind-boggling quality" in a statement by the senator that "one would think the international community would at least condemn the situation and move to stop what appears like genocide."

What's mind-boggling about that? Nothing, it seems to us, if you accept as reasonably accurate even the most restrained accounts of the atrocities that have been -- and presumably still are being -- committed by the savage crew now in control in Phnom Penh. Neither in his original testimony before a Senate subcommittee nor in a speech on Friday did Mr. McGovern offer a very plausible explanation of how the international community could be persuaded to muster a "military force" to "knock this regime out of power"; there is not, to our knowledge, any very good precedent for that sort of international breaking-and-entering -- for even the worthiest purposes.

But it does not seem to us that the senator is duty bound to have precisely the right answers before he can be permitted to raise what are undeniably the right questions -- whether you are talking about the rulers of Cambodia or, let us say, Idi Amin. Still less does it appear to us that Sen. McGovern, the outspoken critic of American military intervention in Indochina, is caught up in some disabling -- and laughable --national military intervention in Cambodia to arrest a program of calculated genocide.

The Journal disagrees, arguing that "one of the few good things to come out of the sordid end of our Indochina campaign was a period of relative silence from the people who took us through all its painful contortions." The "people," in this case, are the liberals who -- The Journal would have us believe -- invented the idea of a "a more vigorous and expansive view of our role as leader in the free world" some 20 years ago, initially involved this country in Vietnam, "blithely" overthrew the Saigon government, then "set about toppling" the American president, and finally wound up "destroying" the American/pro-Western presence in Indochina. Those people, The Journal concludes, "should have the grace to maintain their quiet for at least a little while longer."

Now that's some indictment -- and also a rather sweeping "shut up." For if you are going to shut up everybody who had a hand of some sort in this country's Indochina ordeal, you are not going to be able to stop with the liberals. It was Dwight D. Eisenhower's generous view of America's role as world policeman that led to the original American commitment to South Vietnam. It was that celebrated liberal Richard Nixon (together with his notoriously liberal advisers, Henry Kissinger, Secretary of State William Rogers and Secretary of Defense Melvin Laird) who carried the U.S. war effort to Cambodia, shattering all semblance of political stability, tearing up the countryside, and opening the way for the takeover by the present murderous crew. And it was by impressive majorities in Congress, including conservatives, liberals and all the rest, that the initial Vietnam War effort was originally endorsed and financed -- and then repudiated.

So if you are going to disqualify from current public debate on Cambodia all those who had a hand or a voice at one stage or another, and in one way or another, in this country's Indochina policy in the long and painful years of involvement and disengagement, you are going to have to disqualify just about everybody in active public life at the time, and an awful lot of people actively involved in the conduct of American foreign policy right now.

And that, we submit, is worse than just a truly mind-boggling idea. It cannot even be dismissed as peevish game-playing -- which it is. It is a kind of incitement to American indifference to a genuinely horrible international situation. Sen. McGovern is merely trying, as he puts it, to apply "the old shock treatment" to something that he thinks people, whether they were supporters or critics of the U.S. effort in Indochina, ought at least to be thinking and talking about --say scandalous. And the point is that he's right.